Cascade configuration HP's

Owned by Jonas Cleiren (Unlicensed)
Last updated: Apr 04, 2022 by Dennis De Beuckeleer
4 min read

The templates consist of various cascade configurations of HP’s.

HP - Cascade of 2 HP’s - Parallel storage tank - HP modulation

Working principle

The programmable controller controls the two heat pumps. If the outside temperature is above -10°C and the top of the thermal store is below 40°C, heat pump 1 will start. When heat pump one is running, and the top thermal store sensor drops further, heat pump 2 will start. The two heat pumps are being modulated by a PI-controller using the temperature of the storage tank.

A delay is used to avoid on/off behaviour of the heat pumps. When one of the heat pumps stops working, the heat pump will start again after the delay time has been passed.

Controls

The following settings can be changed by the user in the programmable controller:

  • TempBufferHighSetpoint = 40;
    (= setpoint temperature of the storage tank at the upper side in °C)

  • TempBufferHighHysteresis = 3;
    (= hysteresis temperature of the storage tank in °C)

  • TempBufferHighMin = TempBufferHighSetpoint - TempBufferHighHysteresis;
    (= minimal temperature of the storage tank in °C)

  • TempOutsideMin = -10;
    (= minimal outside temperature in °C)

  • MinModulationHP = 25;
    (= minimal modulation value of the HPs in % )

  • MinModulationHPhysteresis = 5;
    (= hysteresis value of the minimal modulation value in % )

  • TimedelayHPs = 4;
    (= start up delay of HPs in minutes)

 

HP1 is enabled on 3 conditions:

  • The top of the thermal store is below 40°C.

  • Temperature outside higher is than -10°C.

  • Timer HP1 is higher than or equal to the time delay of 4 minutes.

 

HP1 is disabled on 2 conditions:

  • Temperature outside is lower than -10°C.

  • The top of the thermal store is higher than 40°C.

 

HP2 is enabled on 3 conditions:

  • Heat pump 1 is working.

  • The top of the thermal store is below 37°C.

  • Timer HP2 is higher than or equal to the time delay of 4 minutes.

 

HP2 is disabled on 2 conditions:

  • Heat pump 1 isn’t working.

  • The top of the thermal store is higher than 40°C.

 

The on/off valve of HP1 is enabled on 1 condition:

  • Temperature outside is higher than -10°C.

 

The on/off valve of HP1 is disabled on 1 condition:

  • Temperature outside is lower than -10°C.

 

The on/off valve of HP2 is enabled on 2 conditions:

  • The top of the thermal store is lower than 37°C.

  • On/off valve of HP1 is open.

 

The on/off valve of HP2 is disabled on 2 conditions:

  • The top of the thermal store is higher than 40°C.

  • On/off valve of HP1 is closed.

Notices/Remarks

  • The system can be further optimised by doing sensitivity studies. For instance, a sensitivity study can be done for the size of the storage vessel.

  • The user can change the design temperatures, thermal power, end units, etc. Keep in mind that the controls have to be changed as well. This can be done by changing the “settings” in the programmable controller which are listed in the top of the code. After changing the settings, the correct operation has to be checked again. The user should only change the “settings” and nothing else in the code to make sure the correct control strategy is still valid.

  • If the user changes the power of the end-units the thermal capacity of the condenser doesn’t change automatically. The user should implement a correct capacity corresponded with the thermal power of the heat pump.

 

This template was developed with an air source heat pump. To use a ground source heat pump you need to apply the following modification:

  • Change the external temperature by a sine wave to the evaporation temperature of the heat pump

 

More information about the HP can be found in Heat pump.

HP - Cascade of 2 HP’s - Parallel storage tank - HP shift for equal running hours

Idem as the previous template, except for a shifting option between HP’s when the first HP starts. If heat pump 1 has more running hours, heat pump 2 will start the sequence first.

HP - Cascade of 2 HP’s - Parallel storage tank - HP with 2 stages

This template is a combination of template “HP - Cascade of 2 HP’s - Parallel storage tank - HP modulation” and template with HP’s in stages found in HP stagesarchived.

HP - Cascade of 2 HP’s - Serial storage tank - HP modulation

Idem as the template “HP - Cascade of 2 HP’s - Parallel storage tank - HP modulation” except with a thermal store on the return instead of the parallel thermal store.

HP - Cascade of 2 HP’s - Serial storage tank and low loss header - HP modulation

Idem as the previous template, except with a low loss header to ensure a constant flow through the heat pumps.

HP - Cascade of 3 HP’s - Parallel storage tank - HP modulation

Idem as the template “HP - Cascade of 2 HP’s - Parallel storage tank - HP modulation” except with 3 heat pumps instead of 2.